The present invention relates to a method of simultaneously producing two continuous cigarette rods.
Cigarette manufacturing machines for simultaneously producing two continuous cigarette rods are already known, and whereby the continuous rods are fed past a cutting head for simultaneously producing two streams of either plain cigarettes, or cigarette portions from which to form filter-tipped cigarettes.
In addition to the problem, commonly encountered on any type of machine, of producing continuous rods that are homogeneous and of a constant given weight per unit length, a major problem of dual-rod machines of the aforementioned type is that of producing two substantially identical continuous rods, which, when cut, provide for forming substantially identical streams of plain cigarettes or cigarette portions in conformance with strict manufacturing tolerances.
In the past, substantially two methods have been adopted by dual-rod machine manufacturers for overcoming the above problem.
According to one known method, described for example in U.S. Pat. No. 4,372,326, a single stream of shredded tobacco is divided by a movable wall into two secondary streams, each of which is fed in the form of a continuous layer of tobacco on to a respective conveyor. The position of the movable wall is adjusted for regulating the flow rate of the two secondary streams as a function of signals emitted by members for controlling the weight per unit length of the tobacco layers.
Though successfully providing for two tobacco layers of substantially the same weight, the above method fails to provide for simply and rapidly controlling distribution, within the two secondary streams, of the light and heavy tobacco particles, i.e. the volume of the tobacco layers as they are formed on the two conveyors.
The second known method, described for example in Italian Patent Application n. 3662A/88 or British Patent n. 2,240,026, is based on the assumption that, in a stream of shredded tobacco, the characteristics of a portion of relatively limited area cannot possibly differ noticeably from those of a similar adjacent portion of the tobacco stream.
On the basis of this assumption, for producing two substantially uniform, identical tobacco layers, the above method provides for dividing a main stream of shredded tobacco into a number of relatively small secondary streams, and for feeding each secondary stream in each pair of adjacent secondary streams on to a respective tobacco layer conveyor.
This second method also provides for no more than statistical, as opposed to direct, control of the weight and volume of the two tobacco layers.